Wireless power transfer system and wireless power transfer method

Abstract

A wireless power transfer system includes a first transmitter coil, a second transmitter coil and a third transmitter coil arranged such that normal directions to planes of the first, the second and the third transmitter coils are orthogonal to each other in a three-dimensional space, and a controller that controls electric currents supplied to the first, the second and the third transmitter coils such that a synthetic magnetic field vector produced by the first, the second and the third transmitter coils rotates in a plane of rotation at a first angular frequency “ω”, and that a normal vector to the plane of rotation rotates about an axis of rotation perpendicular to the normal vector at a second angular frequency “a” equal to or smaller than the first angular frequency (a≤ω).

What is claimed is: 
     
       1. A wireless power transfer system comprising:
 a first transmitter coil, a second transmitter coil, and a third transmitter coil arranged such that normal directions to planes of the first, the second and the third transmitter coils are orthogonal to each other in a three-dimensional space, and 
 a controller that controls electric currents supplied to the first transmitter coil, the second transmitter coil and the third transmitter coil such that a synthetic magnetic field vector produced by the first transmitter coil, the second transmitter coil and the third transmitter coil rotates in a plane of rotation at a first angular frequency “ω”, and that a normal vector to the plane of rotation rotates about an axis of rotation perpendicular to the normal vector at a second angular frequency “a” equal to or smaller than the first angular frequency, 
 wherein the controller controls a first power source connected to the first transmitter coil to modulate a non-oscillating magnitude (H 0 ) of a magnetic field vector with −sin(at)*cos(ωt), controls a second power source connected to the second transmitter coil to modulate the non-oscillating magnitude (H 0 ) of the magnetic field vector with cos(at)*cos(ωt), and controls a third power source connected to the third transmitter coil to modulate the non-oscillating magnitude (H 0 ) of the magnetic field vector with α*sin(ωt), and wherein a point of the synthetic magnetic field vector continuously moves on a sphere or a spheroid. 
 
     
     
       2. The wireless power transfer system as claimed in  claim 1 ,
 wherein the controller controls a strength of a magnetic field component along a direction parallel to the axis of rotation of the normal vector to 1/√2 times the original strength to make a received power constant. 
 
     
     
       3. The wireless power transfer system as claimed in  claim 1 ,
 wherein the controller controls the first power source such that a first magnetic field component produced by the first transmitter coil in a first direction changes with time in proportion to −sin(at)*cos(ωt), controls the second power source such that a second magnetic field component produced by the second transmitter coil in a second direction perpendicular to the first direction changes with time in proportion to cos(at)*cos(ωt), and controls the third power source such that a third magnetic field component produced by the third transmitter coil in a third direction perpendicular to the first direction and the second direction changes with time in proportion to α*sin(ωt), where α is equal to 1 or 1/√2 (α=1 or 1/√2). 
 
     
     
       4. The wireless power transfer system as claimed in  claim 1 ,
 wherein the wireless power transfer system is configured to transfer electric power to a power receiver with a receiver coil that has a same resonant frequency as the first transmitter coil, the second transmitter coil, and the third transmitter coil. 
 
     
     
       5. The wireless power transfer system as claimed in  claim 4 ,
 wherein an electric power oscillating with period π/a is transferred to the receiver coil. 
 
     
     
       6. A wireless power transfer method comprising:
 setting a first transmitter coil, a second transmitter coil, and a third transmitter coil such that normal directions to planes of the first, the second and the third transmitter coils are orthogonal to each other in a three-dimensional space; 
 placing a power receiver in the three-dimensional space formed by the first transmitter coil, the second transmitter coil, and the third transmitter coil; and 
 controlling electric currents supplied to the first transmitter coil, the second transmitter coil and the third transmitter coil such that a synthetic magnetic field vector produced by the first transmitter coil, the second transmitter coil and the third transmitter coil rotates in a plane of rotation at a first angular frequency “ω”, and that a normal vector to the plane of rotation rotates about an axis of rotation perpendicular to the normal vector at a second angular frequency “a” equal to or smaller than the first angular frequency, 
 wherein the controller controls a first power source connected to the first transmitter coil to modulate a non-oscillating magnitude (H 0 ) of a magnetic field vector with −sin(at)*cos(ωt), controls a second power source connected to the second transmitter coil to modulate the non-oscillating magnitude (H 0 ) of the magnetic field vector with cos(at)*cos(ωt), and controls a third power source connected to the third transmitter coil to modulate the non-oscillating magnitude (H 0 ) of the magnetic field vector with α*sin(ωt), and wherein a point of the synthetic magnetic field vector continuously moves on a sphere or a spheroid. 
 
     
     
       7. The wireless power transfer method as claimed in  claim 6 ,
 wherein a strength of a magnetic field component along a direction parallel to the axis of rotation of the normal vector is controlled to 1/√2 time the original strength to make a received power constant. 
 
     
     
       8. The wireless power transfer method as claimed in  claim 6 , further comprising:
 controlling the first power source such that a first magnetic field component produced by the first transmitter coil in a first direction changes with time in proportion to −sin(at)*cos(ωt); 
 controlling the second power source such that a second magnetic field component produced by the second transmitter coil in a second direction perpendicular to the first direction changes with time in proportion to cos(at)*cos(ωt); and 
 controlling the third power source such that a third magnetic field component produced by the third transmitter coil in a third direction perpendicular to the first direction and the second direction changes with time in proportion to a*sin(ωt), where a is equal to 1 or 1/√2 (α=1 or 1/√2). 
 
     
     
       9. The wireless power transfer method as claimed in  claim 6 ,
 wherein a resonant frequency of a receiver coil of the power receiver is the same as that of the first transmitter coil, the second transmitter coil, and the third transmitter coil. 
 
     
     
       10. The wireless power transfer method as claimed in  claim 9 , further comprising:
 receiving at the power receiver an electric power oscillating with period π/a. 
 
     
     
       11. The wireless power transfer system as claimed in  claim 1 ,
 wherein the non-oscillating magnitude of the synthetic magnetic field vector is constant in all directions, and the synthetic magnetic field vector with a constant magnitude rotates at the first angular frequency “ω”. 
 
     
     
       12. The wireless power transfer system as claimed in  claim 1 ,
 wherein the non-oscillating magnitude of the synthetic magnetic field vector is multiplied by a for the third magnetic vector component, and a locus of the synthetic magnetic field vector moves on the spheroid. 
 
     
     
       13. The wireless power transfer method as claimed in  claim 6 ,
 wherein the non-oscillating magnitude of the synthetic magnetic field vector is constant in all directions, and the synthetic magnetic field vector with a constant magnitude rotates at the first angular frequency “ω”. 
 
     
     
       14. The wireless power transfer method as claimed in  claim 6 ,
 wherein the non-oscillating magnitude of the synthetic magnetic field vector is multiplied by a for the third magnetic vector component, and a locus of the synthetic magnetic field vector moves on the spheroid.